The Genetically Modified Mice Shared Service provides members of the Cancer Center and other University researchers access to transgenic animal technology in a n efficient cost-saving manner. This core allows investigators to use transgenic mice and, beginning in November 1997, the service will be able to assist investigators in producing new mouse mutants by gene targeting in embryonic stem (ES) cells. The service also will provide gene targeting technology for ES cell research. During the last year and a half, services have been expanded by compiling information on other molecularly altered mice that are available. The shared service personnel assist in obtaining the mice and maintaining and screening them. The goal is to help investigators identify or develop models to address their specific cancer research. Since developing or establishing colonies of these special mice is very expensive, the shared service centralizes these efforts, thus reducing some of the large start-up costs that occur when developing animal models. Importantly, this facility allows individuals who have not previously worked with mouse models to be guided in their use. As more investigators have come to realize the power of these systems, use of this service has increased each year, during the first three years of existence.